Schwalbe Thunder Burt Tire - 27.5 x 2.1, Tubeless, Folding, Black, Evolution, Super Ground, Addix SpeedSchwalbe Thunder Burt Tires. The development goal of this tire was to combine the best of the Racing Ralph and Furious Fred. With its many small lugs, it has the grip of the Racing Ralph but the low rolling resistance of the Furious Fred. PaceStar: fast rolling cross country compound with easy rolling base layer, fast center and grippy shoulders Product Specifics Color: Black Defined Color: Black Flat Protection: Sidewall ISO Diameter: 584 650b 27. 5"